This invention relates to nuclear reactors and, more particularly, to a phase-separator assembly for a dual-phase nuclear reactor. A major objective of the present invention is to provide for more efficient installation of a steam separator and a dryer in such a reactor and to provide for more compact storage of said components.
Nuclear reactors generate heat in a fissionable reactor core and transfer this heat by flowing coolant through the core. In dualphase reactors, the flowing coolant stores energy, at least partially, in the form of a phase change, e.g., from liquid to vapor. Since dualphase reactors are primarily boiling-water reactors, the phase change is from water to steam. Herein below, the operation of dualphase reactors generally can be extrapolated from the description of boiling-water reactors.
In a boiling-water reactor, a water-steam mixture rises from the core. The water is to be recirculated down a downcomer and then back up through the core. The steam is to be directed from the reactor for utilization; for example, the steam can drive a turbine, which, in turn, can drive a generator to produce electricity. Steam condenses as it gives up energy to the turbine; the condensate can be returned to the reactor vessel to merge with the recirculating water.
While the separation of water and steam is promoted by gravity, small amounts of steam can be entrained in the recirculating water and small amounts of water can be entrained in the steam exiting the reactor vessel. Both of these phenomena interfere with reactor efficiency. Accordingly, many boiling-water reactors include a steam separator that separates the bulk of the water from the steam/water mixture rising from the core. Steam separators typically leave a small amount of water in the rising steam, so dryers are typically disposed above the steam separators to remove the remaining water.
Both steam separators and dryers remove water from steam. The steam separators provide for gross removal, while dryers provide for fine removal. For example, the mixture rising from the core can be 85% steam by weight. With this input, a steam separator can yield a mixture that is 90% steam by weight. The dryer can convert the output of the steam separator to a steam flow that is better than 99.9% steam.
Since the steam separator and dryer are located above the core, they must be removed during refueling operations to gain access to the core. Typically, during a refueling operation, the top head of a reactor vessel is removed. The dryer is then removed and placed at one location within a storage pool. The steam separator is then removed and placed in another location within a storage pool. Fuel bundles are then replaced. The steam separator is then reinstalled and then the dryer is reinstalled. Finally, the reactor vessel is closed and reactor operation resumed.
Considerable effort and cost are consumed in handling and storing these large, contaminated components. Each transfer of a component such as a steam separator or a dryer is a project in itself. When not in the reactor, steam separators and dryers must be stored and enclosed in shielding material, typically a pool of water in a concrete chamber. The size of the chamber must be adequate to accommodate the components to be stored, and the amount of concrete and safety equipment required to service the chamber grows geometrically with the size of the chamber. Thus, reactor plant manufacturing costs and maintenance costs are severely impacted by the size of components such as steam separators and dryers. What is needed is a system that provides the functions of a steam separator and a dryer while requiring fewer component transfers and less storage space.